Winglets provide a means to reduce the negative effects of lift-induced wing drag by effectively increasing the length of the trailing edge of the wing. The effective increase in the length of the trailing edge may spread out the distribution of the vortices that are shed by the trailing edge and the wing tip as the wing flies through the air. The re-distribution of vortices may reduce aerodynamic losses from lift-induced drag. Advantageously, winglets may provide an increase in effective trailing edge length without increasing the length of the wing leading edge. In this regard, by adding winglets to the wings instead of increasing the wing span in the conventional manner, the added weight, cost, and complexity associated with the lengthening of leading edge lift-enhancement devices (e.g., slats, Krueger flaps) may be avoided.
Conventional winglets are fabricated as a hybrid assembly of components formed of different materials. For example, conventional winglets may be comprised of composite spars and skin panels that may be joined to a metallic leading edge and a metallic trailing edge, and which may include metallic attach fittings. Unfortunately, the assembly of the winglet components is a time-consuming and labor-intensive process requiring a large quantity of mechanical fasteners. The large quantity of fasteners may increase the overall weight of the winglets. In addition, specialized tooling may be required for maintaining the relative positions of the components during fastener installation.
Furthermore, fasteners that are installed in the outer mold line (OML) surface of the winglets may disrupt the airflow passing over the OML surface. The disruption in airflow may minimize the distance over which the airflow is maintained in a laminar state before the airflow becomes turbulent with a resulting increase in aerodynamic drag. For example, in conventional winglets, the distance over which the airflow is laminar may be limited to approximately 10% of the chord length, with the downwind airflow becoming turbulent over the remaining portion of the winglet. The increase in aerodynamic drag due to turbulent airflow over the winglet may limit the gains in aircraft fuel efficiency that would be possible if the airflow were maintained in a laminar state over a longer portion of the winglet chord length.
As can be seen, there exists a need in the art for a winglet configuration that maintains the air flow in a laminar state over a relatively large portion of the chord length prior to the airflow becoming turbulent.